1. Field of the Invention
The invention relates to a system for detecting when a web is not being completely perforated, cut, scored or otherwise weakened at spaced intervals along its length, and more particularly to a web perforating system that detects and indicates when a perforator in a rewinder or similar machine is operating with a broken or dull perforating blade.
2. Description of the Prior Art
During the production of paper products such as toilet tissue and paper towel rolls, a paper web is unwound from a parent roll by a rewinder as is well known in the art. As the paper web enters the rewinder, it contacts one or more rolls which deliver it to a web cutting apparatus or xe2x80x9cperforatorxe2x80x9d that is equipped with a perforating roll. One such perforator is disclosed in U.S. Pat. No. 2,870,840 to Kwitek which is hereby expressly and completely incorporated by reference. The perforator includes a perforating roll carrying rows of perforating blades or xe2x80x9cfly knives.xe2x80x9d These rows are spaced from each other along the circumference of the perforating roll. The perforating blades rotate relative to and cooperate with stationary anvils that carry anvil blades. The anvils are secured in a helical pattern to a perf anvil head which extends across the path of travel of the web. The perf anvil head in such a device can rotate relative to the perforating roll between an open position and an operating position. In an open position, the perf anvil head spaces the anvils from the perforating blades so that the web will not be perforated. When the perf anvil head is rotated into the operating position, the perforating blades contact the anvil blades and perforate the passing web, thereby creating perforations at predetermined spaced intervals in the passing web. After the web passes through the perforator, it moves to a winding system which winds it onto a core.
A perforating roll can rotate at speeds typically up to 1500 feet per minute. As a result, the perforating blades experience high compressive and shearing forces when they contact the stationary anvil blades. These forces can cause a perforating blade to fail at any time during a production run. Additionally, over time, the teeth of a perforating blade can dull as a result of repeatedly impacting an anvil blade. When the perforator operates with a broken or dull blade, it may not fully perforate the web. As a result, rolls of paper products which are not fully perforated will be sent to the customer. Paper rolls with incomplete perforations are the largest complaint of perforated product customers.
Perforating machines such as that discussed above lack a system for detecting if a perforating blade has broken or become so dull that it does not perforate the passing web. Instead, perforated paper producers rely on an operator to visually inspect the perforations between sheets of a wound paper product at regularly spaced time intervals, such as every hour. Between these inspections, a broken blade may only be detected if the operator hears a noise which suggests that a blade has broken. As difficult as it is for an operator to hear when the perforator is operating with a broken blade, it is virtually impossible to detect if it is operating with a dull blade without visually inspecting the perforated rolls.
If a perforating blade breaks or becomes too dull to properly perforate the web at any time between visual inspections, the machine will continue to operate and produce incomplete perforated products until at least the next visual inspection. For example, if the operator stops and examines the results of the perforating process every hour, a blade that breaks fifteen minutes into a run will cause the perforator to produce forty-five minutes worth of improperly perforated sheet product. This can add up to a significant amount of improperly perforated product when the rewinder is operating at 1500 or more feet of paper web per minute. Additional problems associated with visual inspection are the loss of production time if the line is shut down while the visual inspection is performed, and the waste of the product that is used for the inspection.
Various machines have included systems to detect when a web has not been properly prepared. One such system is disclosed in U.S. Pat. Nos. 4,813,320 and 5,091,962 to Malloy et al. which disclose a stamping machine having an associated sensing device for determining when a stamped web has been incorrectly fed. After the web is stamped, it passes from the press to a sensing device which includes an internal coil for generating an electromagnetic flux field. The sensing device produces a waveform which is based upon the amount of metal in the web and the position of the stamped portions relative to the sensors. This waveform is compared to a reference waveform. If a deviation exists between the waveforms, this indicates that the web was incorrectly fed. The stamping machine is then stopped and the position of the web is corrected. However, since the sensing device is spaced away from the press, the press will continue to stamp the incorrectly fed web and create waste for the length of time that it takes the frame with the first perceptible amount of deviation to reach the sensor.
U.S. Pat. No. 3,339,434 to Sparling discloses a drill press including a monitoring apparatus that generates a control signal when the drill bit is broken or dull. The monitoring apparatus measures the duration of each drilling cycle and compares it with a reference cycle. Extended cycle times are caused by broken or dull drill bits taking longer to contact a reference point, such as the work piece, than a normally operating drill bit. When the measured cycle exceeds the reference cycle, a control signal is generated, indicating that a problem exists with the process. An apparatus which uses a timing cycle for monitoring a plurality of drill bits is also disclosed.
U.S. Pat. No. 2,792,833 to Pokorski discloses an automated cutting press that forces a cutting die through a sheet material until it contacts a cutting block. The reciprocating die and cutting block include electrically conductive surfaces. A detection system establishes a circuit when the die and cutting block contact each other. The circuit affects the retraction of the die to its starting position so that the cycle can be repeated. This system is designed to automate the operation of the press, not to detect the presence of a broken tool. Additionally, this system will operate with a broken tool, as long as the tool can be forced through the sheet material and at some time contact the cutting block. This can result in a substrate cut that is not properly sized or shaped.
It is an object of the present invention to overcome the drawbacks associated with the prior art rewinders and perforators.
It is also an object of the present invention to provide a perforator that detects and indicates when one of its blades breaks or becomes so dull that it cannot properly perforate a web.
A further object of the invention is to provide a method for detecting when a perforator is operating with a broken or dull perforating blade.
The present invention provides a web perforating apparatus which includes a system for detecting and indicating when a blade in the apparatus is broken, dull or otherwise not making contact with an opposing blade and thereby not perforating the web. This apparatus is typically used with rewinders or other similar machines that produce perforated sheets of products, such as paper, using sets of stationary anvil blades and rotating perforating blades. The perforating blades are typically attached to a bed roll and rotate relative to the anvil blades. These anvil and perforating blades are finely adjusted to make light, accurate contact with each other. As the perforating blades contact the web extending across the anvil blades, perforated product is produced. The anvil blades are solid in profile shape and connected to a movable mounting bar by blade holders. The blade holders secured to the rewinder also hold electric conductors for supplying a low amperage current to the anvil blades. The anvil blades and conductors are insulated from the grounded blade holders and the remainder of the machine base so the applied current does not go to ground.
The electric current is used to detect when the perforating blade is not extending through the web and contacting the anvil blade. As the grounded perforating blades make contact with the current carrying anvil blades, a closed circuit is formed, a signal is generated and a representation, such as a waveform is produced. When all the perforating blades properly contact the anvil blades, a xe2x80x9cnormalxe2x80x9d waveform is produced and recorded. If a perforating blade is broken, the recorded waveform will include an anomaly. The presence of the anomaly can be transmitted to the machine operator via a flashing light, siren etc. When an anomaly is detected, the machine can be quickly, if not immediately or automatically, shut down and the broken blade changed so as to reduce the amount of unperforated product. This detection system prevents a broken blade from unknowingly being used during the production of perforated paper product.
In an embodiment of the present invention, the apparatus comprises at least one anvil including a blade holder and an anvil blade which is positioned within the blade holder. The blade holder is formed of an insulating material for electrically isolating the anvil blade from the machine frame of the rewinder. An electrical conductor is coupled to the anvil blade for supplying an electric current to the anvil blade from a current source. The apparatus also includes at least one grounded perforating blade for moving relative to the at least one anvil blade and cooperating with the at least one anvil blade to perforate the web at predetermined points along its length. The at least one perforating blade will contact the anvil blade after perforating the web. A closed circuit is formed and maintained along the at least one anvil blade as long as the perforating blade remains in contact with the anvil blade. Since the anvil blades are on a spiral mount, their contact with the perforation blades is progressive. This results in progressive single point contact between the perporation and anvil blades along the length of the anvil blades. The apparatus further includes means for detecting if a closed circuit has been formed and maintained along the anvil blade when the perforating blade moves into a position where it should make contact with the anvil blade.
The present invention also includes a method for perforating a web using a perforating apparatus and detecting when the web is not being completely perforated. The method comprises the steps of grounding a first blade of the perforating apparatus, electrically isolating a second blade of the perforating apparatus from a ground and connecting the isolated second blade to an electric current source. The method also includes moving one of the blades relative to the other blade so at least a portion of the first blade contacts a portion of the second blade, and creating a closed circuit at points along the second blade where contact is made between the second blade and the first blade. A step of generating a signal which represents where closed circuits were created along the second blade also forms part of the present invention. Additionally, the method can include the steps of comparing the generated signal to a reference signal, and indicating to an attendant when the generated signal differs from the reference signal.
According to the present invention, an operator will be notified and the perforation run stopped as soon as a broken or dull blade is detected, thereby keeping the amount of unperforated product to a minimum. This will significantly reduce waste and down time by doing away with the need to shut down the run to visually inspect the blades and the need to unroll the produced product to visually inspect the perforations or lack thereof. Moreover, rolls of completely perforated paper can be critical to the operation of dispensers which use the perforation rows to recognize the leading edge of a sheet in order to either begin or stop the paper dispensing process. Proper perforation rows also facilitate clean and complete separation of the sheet when pulled by user.